Post nested params (hash) using HTTPClient - ruby

Question

I needed a to have a multipart http post from one app to another that included a file attachment and a nested params hash. I tried using HTTPClient which worked for the file attachment, however I could not get params to send in a nested format.
data_params = Hash.new
data_params[:params] = Hash.new
data_params[:params][:f] = Hash.new
data_params[:params][:d] = Hash.new
data_params[:params][:d][:name] = "Mich"
data_params[:params][:d][:city] = "Ostin"
data_params[:params][:f][:event] = "Sundance"
http_client = HTTPClient.new
body = data_params[:params]
response = http_client.post('http://localhost:3030/receiver/receive_test_data/', body)
with the receiver app seeing the params as {"d"=>"nameMichcityOstin","f"=>"eventSundance"} (with the hash collapsed into strings on the nested level)
I wonder if this is a limitation on http posts or am I simply doing something wrong. I have worked with JSON before, which I know supports a nested structure, but there I have no idea how to add file attachments. I appreciate any suggestions or alternative methods that would comply with 'best practices' on doing something like this.

Answer 1

If using Rails:
> {:a=>53,:b=>{:c=>7}}.to_query
=> "a=53&b[c]=7"
http://apidock.com/rails/ActiveSupport/CoreExtensions/Hash/to_query

Answer 2

I'm not sure which HTTPClient library you're using so I haven't been able to try this, but what if you use keys like this
data_params[:params]['d[name]'] = "Mich"
data_params[:params]['d[city]'] = "Ostin"
i.e. data_params[:params] is just a one level hash.
and then the receiving application will unpack this into the nested hash that you expect.